Looking at the chi-squared results, there is a significant difference between all three sample habitats in the high and low altitude areas. There is also a significant difference when these habitats are grouped together and classed simply as two separate groups to compare the difference between the high and low altitudes. Based on the statistical findings, we can reject the null hypothesis of ‘there is no significant difference in the distribution of different colours and banded snails found at high and low altitudes’. Our initial aim was to examine colours and bands, looking at how these varied at the different altitudes. However, when analysing the data, there was no strong correlation between altitude and number of bands so it seemed more appropriate to investigate the link between colour and altitude.
Although, the experiment was to compare the differences in the populations at the high and low altitudes, when analyzing the results it became clear that there was also variation between the different populations at the same altitude. Due to the fact that we collected the samples from the same habitat type, this variation can’t be due to selection leading us to conclude that it must be due to genetic drift.
With these sample groups living in the same habitats at the same altitude, it could be hard to comprehend the difference in phenotype variation. However, taking into account the sedentary lifestyle of Cepea Nemoralis, it is easy to assume that there will be little gene flow between populations living more than a few metres apart. This degree of local genetic differentiation is known to occur with C.nemoralis due to frequent bottlenecks and founder effects. Another factor that contributes to this is the strong random genetic drift not being counterbalanced by gene flow (Le Mitouard, Bellido, et al, 2010).
Another theory for the evolution of morphological area effects could be environmental selection by microclimatic features (Ochman, Jones, et al. 1983). This would mean that each of our sample groups would be living in their own specific microhabitat and would not be geographically isolated. This would mean the differing morphological features of the populations would not be caused by genetic drift but in fact natural selection in habitats that appear to be very similar but could be affected by microclimatic aspects.
Natural selection could also be a contributing factor to the morphological differences in the high and low altitude populations of C.Nemoralis. The climatic differences between the two altitudes could include factors such as temperature, moisture and air-pressure.
When looking at the factor of temperature, previous experiments have proved that the pink shelled snails are least resistant to different temperatures (Lamotte, 1959 in Cameron, 1969). Looking at our results there was no significant difference in the percentage of pink shelled snails at the high or low altitudes, leading to the conclusion that it is not temperature which is causing the morphological variation.
Another climatic factor is rainfall; studies have shown that with higher rainfall the frequency of yellow morph snails decreases (Mazon et al, 1987). The populations we were sampling were present at the top and bottom of a large hill, meaning that snails at the bottom of the hill are more likely to encounter more rain due to the steep incline which causes an accumulation of water at the bottom of the hill.
The main drawback in this experiment was that it may not be an accurate reflection of the results throughout the year. This is because the climate, rainfall, temperature, etc may vary depending on the time of year. If we were to do the experiment again we would try to do more repeats in each habitat and would include other snail species to make our results more reliable.
CAMERON, R.A.D 1969, THE DISTRIBUTION AND VARIATION OFCEPAEA NEMORALIS L. NEAR SLIEVEGARRAN,COUNTY GLARE AND COUNTY GALWAY,EIRE. Proceedings of the Malacological Society of London, 38, 439-450 Chat conversation end
Le Mitouard, E, Bellido, A, Guller, A, Madec, L, (2010) ‘Spatial structure of shell polychromatism in Cepaea hortensis in relation to a gradient of landscape fragmentation in Western France.’ Landscape Ecology, Vol. 25, Issue 1, 123-134 MAZON, L. I., M. PANCORBO, M. A., VICARIO, A., AGUIRRE, A. I., ESTOMBA, A. AND LOSTAO, C. M. 1987, Distributionof Cepaea nemoralis according to climatic regions in Spain.Her
Although, the experiment was to compare the differences in the populations at the high and low altitudes, when analyzing the results it became clear that there was also variation between the different populations at the same altitude. Due to the fact that we collected the samples from the same habitat type, this variation can’t be due to selection leading us to conclude that it must be due to genetic drift.
With these sample groups living in the same habitats at the same altitude, it could be hard to comprehend the difference in phenotype variation. However, taking into account the sedentary lifestyle of Cepea Nemoralis, it is easy to assume that there will be little gene flow between populations living more than a few metres apart. This degree of local genetic differentiation is known to occur with C.nemoralis due to frequent bottlenecks and founder effects. Another factor that contributes to this is the strong random genetic drift not being counterbalanced by gene flow (Le Mitouard, Bellido, et al, 2010).
Another theory for the evolution of morphological area effects could be environmental selection by microclimatic features (Ochman, Jones, et al. 1983). This would mean that each of our sample groups would be living in their own specific microhabitat and would not be geographically isolated. This would mean the differing morphological features of the populations would not be caused by genetic drift but in fact natural selection in habitats that appear to be very similar but could be affected by microclimatic aspects.
Natural selection could also be a contributing factor to the morphological differences in the high and low altitude populations of C.Nemoralis. The climatic differences between the two altitudes could include factors such as temperature, moisture and air-pressure.
When looking at the factor of temperature, previous experiments have proved that the pink shelled snails are least resistant to different temperatures (Lamotte, 1959 in Cameron, 1969). Looking at our results there was no significant difference in the percentage of pink shelled snails at the high or low altitudes, leading to the conclusion that it is not temperature which is causing the morphological variation.
Another climatic factor is rainfall; studies have shown that with higher rainfall the frequency of yellow morph snails decreases (Mazon et al, 1987). The populations we were sampling were present at the top and bottom of a large hill, meaning that snails at the bottom of the hill are more likely to encounter more rain due to the steep incline which causes an accumulation of water at the bottom of the hill.
The main drawback in this experiment was that it may not be an accurate reflection of the results throughout the year. This is because the climate, rainfall, temperature, etc may vary depending on the time of year. If we were to do the experiment again we would try to do more repeats in each habitat and would include other snail species to make our results more reliable.
CAMERON, R.A.D 1969, THE DISTRIBUTION AND VARIATION OFCEPAEA NEMORALIS L. NEAR SLIEVEGARRAN,COUNTY GLARE AND COUNTY GALWAY,EIRE. Proceedings of the Malacological Society of London, 38, 439-450 Chat conversation end
Le Mitouard, E, Bellido, A, Guller, A, Madec, L, (2010) ‘Spatial structure of shell polychromatism in Cepaea hortensis in relation to a gradient of landscape fragmentation in Western France.’ Landscape Ecology, Vol. 25, Issue 1, 123-134
MAZON, L. I., M. PANCORBO, M. A., VICARIO, A., AGUIRRE, A. I., ESTOMBA, A. AND LOSTAO, C. M. 1987, Distributionof Cepaea nemoralis according to climatic regions in Spain.Her